Astronomy 04 The Solar System Chapter 8: "Earth as a Planet"

Earth is a unique planet in many ways: Life exists on Earth surface. Earth has large amounts of liquid water on its surface. Earth has oxygen in its atmosphere.

Earth is a unique planet in many ways: Earth surface is constantly being renewed through the process of Plate Tectonics. Earth has a strong magnetic field.

Four Stages of Planetary Formation: Condensation Accretion Planetesimals Protoplanet

Four Stages of Planetary Development: Differentiation Cratering Flooding Surface Evolution

Differentiation Early in Earth’s history when it was still totally molten, materials separated according to density. Metals such as iron (Fe) and nickel (Ni) sank to the center while light rocky materials like silicates (Si) floated to the surface.

Four Stages of Planetary Development: Differentiation Cratering Flooding Surface Evolution

Cratering After Earth had cooled and a crust had formed, a heavy bombardment of planetesimals and meteorites blasted its surface forming craters.

Four Stages of Planetary Development: Differentiation Cratering Flooding Surface Evolution

Flooding Molten lava flowed through cracks in Earth’s crust produced by planetesimal impacts. Huge amounts of vapor in the atmosphere condensed and torrential rains fell, drained off the continents and formed the first oceans.

Four Stages of Planetary Development: Differentiation Cratering Flooding Surface Evolution

Slow Surface Evolution Air and water erosion along with shifting continental plates constantly changed the appearance of Earth over the last 3.5 billion years.

Earth’s magnetic field protects it from the solar wind. The rotation of Earth’s highly-conductive iron nickel core generate the magnetic field in a process called the dynamo effect.

Chapter 20: “Planet Earth” Earth’s magnetic field protects it from the solar wind.

The surface where the solar wind is first deflected by Earth’s magnetic field is called the bow shock. The cavity in the solar wind generated by Earth’s magnetic field is called the magnetosphere.

High energy particles from the solar wind trapped within the magnetosphere produce the Van Allen belts.

The magnetic field of Earth acts with the solar wind to produce the colorful aurora.

The crust of Earth is broken up into huge pieces called plates. The theory that deals with the origin and motion of these plates is called plate tectonics.

The huge cracks in Earth’s crust that separate plates are called faults. Here we see the famous San Andreas fault which runs just to our west through the Santa Cruz Mountains.

Plates are formed along regions called “midocean rifts” where lava wells up from below. Near the rifts, Earth’s crust is pulling apart at the rate of 2-4 cm per year.

In other places, sections of the crust are pushed below the continents into subduction zones. This process builds mountains and volcanoes.

Rocks that form near the the midcoean rifts are solidified lava called basalts.

One of the marks of plate tectonics is folded mountain chains. Crustal plates can also split apart to open new seas. The first sign of such splitting is a long, straight, deep depression called a rift valley.

About 250 million years ago all continents belonged to a single land mass called Pangea. Gradually the plates drifted apart from each other forming the land masses we know today.

The first atmosphere of Earth called the primeval atmosphere consisted of hydrogen, helium, methane and ammonia. A secondary atmosphere was formed as Earth cooled through the process of outgassing. It consisted of carbon dioxide and water vapor. When plant life appeared on Earth, carbon dioxide was oxygen was produced through the process of photosynthesis.

Oxygen reacted with sunlight to produce ozone gas which shielded Earth from lethal short wavelength radiation from the Sun and set the stage for the appearance of animal and human life.

Today, humans are releasing large amounts of greenhouse gases into the atmosphere which may be resulting in global warming. This warming is due to the greenhouse effect.